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Three different morphologies of tungsten oxides, nanoparticles, nanosheets and hierarchical microspheres, have been successfully synthesized by a facile carboxyl-directed hydrothermal process. The chelation of carboxylic groups with W(OH)6 nuclei is recognized to be the origin of the morphological change. Gas-sensing measurements reveal that the sensing performance varies with WO3 morphology, and the hierarchical WO3 not only exhibits high sensitivity and fast response but also has low operating temperature to toxic NO2. The response of hierarchical WO3 is nearly 2 times and 10 times higher than those of the nanosheets and nanoparticles, respectively. The maximum response of hierarchical WO3 reaches 319 to 10 ppm NO2 at 200 °C. A relationship between morphology and crystal defect is established based on photoluminescence analysis. It is demonstrated that the change in defect feature in crystalline WO3 is responsible for its morphology-dependent gas-sensing properties. [ABSTRACT FROM AUTHOR]

Zero-dimensional Fe2O3 nanoparticles were successfully decorated on three-dimensional WO3 architectures to constitute a photocatalyst of Fe2O3@WO3 heterojunction. The obtained samples were characterized in detail by X-ray diffraction, scanning electron microscopy, elemental mapping, X-ray photoelectron spectroscopy and UV-Vis absorption spectra. The results indicate that rhombohedral α-Fe2O3 nanoparticles are homogeneously decorated on the surface of monoclinic WO3 architectures, and the constituted n+-n heterojunction results in "redshift" of the optical absorption. The photocatalyst of 1%Fe2O3@WO3 annealed at 400 °C exhibits the highest photocatalytic activity for degradation of Rhodamine B under visible light irradiation. The degradation obeys first-order reaction kinetics with an apparent rate constant of 0.057 min-1. It is suggested that the potential-energy difference between Fe2O3 and WO3 accelerates the separation of photogenerated electron-hole pairs, dominating the enhanced photocatalytic activity. The results presented herein provide new insight for development of a novel visible-light-driven photocatalyst and its potential application in harmful pollutant degradation. [ABSTRACT FROM AUTHOR]